The present invention relates to an electromagnetic sound generator for generating sounds by vibrating a vibration plate by an electromagnet, and more particularly to an electromagnetic sound generator mounted on a printed circuit board by the surface mount technology.
In recent years, there is a tendency to mount small electric parts on a printed circuit board, the electromagnetic sound generator as a small buzzer is accordingly mounted on the printed circuit board. Such a printed circuit with the electromagnetic circuit board is used as a signaling device of the portable telephone and beeper.
Referring to FIGS. 5 and 6, which are a plan view of a conventional electromagnetic sound generator and a sectional view taken along a line Axe2x80x94A of FIG. 5 respectively, a case 50 of the electromagnetic sound generator comprises a lower case 51 and an upper case 52.
The lower case 51 has a circular bottom 51d and a cubic portion 51e. An annular projection 51a is formed on the lower case 51 and a pair of cylindrical projections 51f, each having a hole 51b are formed in the cubic portion 51e. 
A yoke 53 made of magnetic material is secured to the bottom 51c. A core 53a is formed at a central portion of the yoke 53 and a notch 53b is formed at a side of the yoke. An annular magnet 55 and a coil 54 are mounted on the yoke 53. An annular vibrating plate 56 having an armature 57 is secured on the annular projection 51a. Thus, a magnetic circuit for a buzzer is formed by the yoke 53, core 53a, magnet 55, and vibrating plate 56.
A pair of lead plates 58, each of which is made of an elongated metal plate, are embedded in the lower case 51. Each of the lead plates 58 is extended between a side wall of the lower case 51 adjacent the hole 51b and an end 58a exposed in the notch 53b of the yoke 53. A coil spring 59 is inserted in each hole 51b. An upper end 59a (FIG. 7a) of the coil spring 59 is inserted in a hole 58c formed in an end portion 58b of the lead plate 58 and electrically connected to the lead plate 58 by solder 65 (FIG. 7b). The lower end of the spring 59 is projected from the underside of the lower case 51.
Both ends of the coil 54 are soldered to ends 58a of lead plates 58. Thus, the coil 54 is connected to the coil springs 59.
The upper case 52 has a sound emanating hole 50a. The upper case 52 is adhered to the lower case 51 so that a resonance room 66 is formed in the case 50.
Here, it is necessary to accurately assemble the coil spring 59 in the hole 51b so as not to contact with the inner wall of the hole 51b. FIGS. 7a and 7b are sectional views showing a method for assembling the coil spring. A positioning jig 70 is provided for positioning the lower case 51. The positioning jig 70 has a pair of positioning holes, each comprising a spring positioning hole 70a and a projection positioning hole 70b. 
In the assembling of the coil spring 59, the lower case 51 is mounted on the jig 70, engaging the cylindrical projection 51f with the projection positioning hole 70b as shown in FIG. 7a. The coil spring 59 is inserted in the spring positioning hole 70a of the jig 70 and the hole 51b of the lower case 51. The upper end 59a of the coil spring 59 is inserted in the hole 58c of the end portion 58b of the lead plate 58 and the coil spring is compressed by a pressing jig 71. The upper end 59a of the coil spring 59 is connected to the end portion 58b by the solder 65 as shown in FIG. 7b. 
Referring to FIG. 8a, the case 50 is mounted on a printed circuit board 81. The end of the coil spring 59 is pressed against a terminal on the circuit board 81 so that the electric current is applied to the coil 54 to vibrate the vibrating plate 56. The generated sound is emanated from the sound emanating hole 50a. 
If the case 50 is inadvertently lifted and there is formed a gap G between the lower end of the cylindrical projection 51f and the printed circuit board 81 as shown in FIG. 8b, the coil spring 59 expands accordingly. Consequently, the connection between the coil spring and the circuit of the circuit board 81 is kept.
FIG. 9 is a sectional view showing a connecting portion of another conventional buzzer. A U-shaped connecting spring pate 62 is connected to a lead frame 61 secured to a case 60 of the buzzer by solder 63 at an end thereof. Another end of the spring plate 62 is pressed against a terminal of a printed circuit board 82.
When the case 60 is mounted on a circuit board 82, the connecting spring plate 62 is bent and the end of the plate is contacted with a terminal of the circuit board 82.
Therefore, if there is formed a gap between the case 60 and the circuit board 82, the contact of the spring plate 62 with the terminal is kept.
However, when each of the above described conventional sound generators falls and collides with a hard ground, the coil spring 59 or spring plate 62 disengages from the terminal. Furthermore, there must be provided a plurality of jigs for accurately soldering the coil spring or spring plate, which requires multiple manufacturing steps.
An object of the present invention is to provide an electromagnetic sound generator having an external connecting terminal structure which has a high reliability and may be simply manufactured without accuracy jigs.
According to the present invention, there is provided an electromagnetic sound generator having a case provided with a yoke, a magnet, a vibrating plate and a coil, and a pair of leads, wherein an end of each of the leads is connected to an end of the coil and the other end of the leads is secured to the case so as to be connected to an outside terminal, a terminal connecting device is provided for connecting the end of the lead to the outside terminal, the terminal connecting device comprises a cylindrical case secured to the case, a connecting rod slidably mounted in the cylindrical case, and a coil spring provided in the cylindrical case to outwardly urge the connecting rod so as to be contacted with the outside terminal at an end of the rod, and means for contacting the cylindrical case with the end of the lead.
The means is engagement of the cylindrical case with a inside wall of a hole formed in the case so as to keep the contact of the cylindrical case with the end of the lead.
The means comprises a ball provided with the cylindrical case so as to be outwardly urged by the coil spring to be contacted with an inside wall of a hole formed inn the end of the lead.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.